1. Field of the Invention
The present invention relates to the thermal management of electronic devices and, in particular, to the use of phase change material as a heat sink for an electronic component.
2. Description of the Related Art
Heat transfer in electronic systems has become a critical design parameter as module level heat transfer has increased exponentially making current cooling technologies inadequate. Indeed, thermal management of electronic devices has become an extremely important field as miniaturization technology has advanced, creating very high heat fluxes at the module level. Further, the performance and reliability of electronic devices are dependent on the maintenance of suitable operating temperatures and a minimization of temperature variations. Therefore, heat generated in a module during normal operation must be continuously removed in order to maintain individual electronic components at approximately constant temperatures for optimum operation. Peak loads which can cause a sudden temperature rise also occur from time to time and it is critical that the cooling system be capable of handling such transient loads.
Commonly used heat removal systems include conductive heat sinks, cold plates, direct impingement cooling systems and heat pipes. However, most methods of electronics cooling are fast approaching their limits in view of the recent advances in large scale integration.
Passive temperature control units using phase change materials have been used in the past. The heat generated in the electronic package is absorbed primarily by the melting of the phase change material with some additional sensible heat absorption by the liquid phase of the phase change material.
Honeywell Corporation uses a heat transfer fluid in a plastic bag as a heat removal and temperature control unit. An example of a suitable heat transfer fluid in that structure is 3M fluorinert (FC77). In the case of this device, however, natural convection heat transfer is limited by the properties of the heat transfer fluid.
Active temperature control units are also commonly used. For example, high power electronic components or high density electronic assemblies are often cooled using cold plates 16 brazed to the bottom of the chip assemblies 18 (see FIG. 1). Heat transferred to the cold plates by conduction is removed by forced convection to air which flows through at 20, or for higher heat fluxes, to a liquid coolant such as water.